To answer your question I have to provide a little history.
Up until 1965, Mass was celebrated everywhere in the Catholic church in Latin according to the “rite” (order or ritual or worship) determined at the Council of Trent and issued by Pope Pius V in 1568.
The Second Vatican Council wrote a “Constitution on the Sacred Liturgy” (1963) which advocated that Mass be celebrated in the native language (“vernacular”) of a particular region or country. This was so that “the Christian people, so far as possible, should be able to understand (the texts and rites) with ease and take part in them fully, actively, as befits a community.”
This document also asked for a revision of the liturgy of the Roman (Latin) Rite. In this revision, the text of the Mass was simplified, and much repetition was eliminated. In some ways the revision brought a return to the way in which the Mass was celebrated at an earlier time in the Church’s history–for example, with the priest facing the people for most prayers, and the people having the option to receive communion in the hand as well as on the tongue. The new order of the Mass was called “the Mass of Pope Paul VI” (named for the leader of the Catholic Church at that time) which replaced the “Mass of Pope Pius V”, also known as the “Tridentine (for the Council of Trent) Mass. The “new” Mass developed gradually as first some prayers, and then all, were prayed in the native language.
Initially the understanding was that some of the Mass in the Roman Rite, particularly the Eucharistic Prayer, would continue to be spoken in Latin. But the move to the native languages was so popular and so effective in encouraging participation in worship that it soon became an almost universal practice to pray all the prayers of the Mass in the native tongue.
There wre a few people, however, who never accepted with comfort the new liturgy. Some believed that it represented a serious break with the older tradition. Others simply felt more at home praying and worshipping in the language and forms which they had known throughout their lives.
Pope Paul VI believed that it was important as an expression of the unity of the Church for all Roman Catholics to adopt the new liturgy. A survey of the bishops of the world in 1981 indicated that the new Mass, including the use of the vernacular, had been widely and favorably accepted as the Catholic way of worship.
Pope John Paul II, however, provided for exceptions to be made to allow for the celebration of the Tridentine Mass for those who could not otherwise attend Mass in good spirit. Permission for this can be given by the local bishop. At first this exception was only allowed for private chapels and not for parish churches, but this was changed in 1988, and many dioceses now have at least one parish where the Tridentine Mass is celebrated. Pope John Paul II made clear, however, that the Mass of Pope Paul VI remains the official liturgy of the church and that all Catholics must accept it as such and not preach or talk against it.